In certain mechanical systems it is desirable to accurately and rapidly sense the temperature of a fluid and to simultaneously sense a pressure of the fluid at the same location. For example, in certain fuel injected gasoline engines, it is desirable to rapidly measure temperature and pressure of fuel at particular locations within one or more fuel injection pathways.
Traditionally, temperature sensors include a thermistor to measure a temperature of a fluid. In many mechanical systems such as gasoline engines. Traditional pressure sensors generally include a diaphragm type pressure sensing element, or a piezo-electric pressure sensing element. Temperature and pressure sensing elements are generally enclosed within a protective sensor package for protection from environmental forces and corrosive effects of the media being measured.
Thermistors and pressure sensors are generally enclosed within standard sensor packages, which are adapted for threading into standard sized mounting holes. Temperature and pressure sensors used in the automotive industry typically include standard connector configurations for mating to standard automotive connectors.
Combined temperature and pressure sensing devices can include a temperature sensor such as a thermistor and a pressure sensor such as a piezo-electric pressure sensing element within a shared sensor package.
The protective package of a sensor in which a temperature and/or pressure sensing element is contained can detrimentally affect the accuracy and response time of the sensor. For example, protective walls of a sensor around a thermocouple create a thermal barrier between the thermocouple and the fluid media being measured. The thermal barrier substantially delays the response time of the thermocouple. Moreover, in a combined temperature and pressure sensor, the temperature sensing element and pressure sensing element are necessarily displaced some distance from each other. Large displacements between a temperature sensing element and a pressure sensing element prevent the sensor from measuring a temperature and sensor at the same location, as desired in many applications. Also, in certain applications, a substantially off-center sensor can be disadvantages because an off-center sensor element could be deployed in a different location depending on how it tightly the sensor body is threaded into a mounting hole, for example.
Previously known combined temperature and pressure sensors have incorporated various sensor port geometries to improve response time and reduce displacement between pressure and temperature sensing elements, while maintaining a substantially centered location of pressure and temperature sensors.
For example, U.S. Pat. No. 8,038,345 to Stoll et al. entitled Sensor Plug for Combined Pressure and Temperature Measurement describes a sensor plug for temperature and pressure measurement in which a temperature sensor and a pressure sensor are disposed substantially concentrically on the sensor body axis. In order to locate both the temperature sensor and the pressure sensor on the sensor body axis, temperature sensing element orifice has an axis that is inclined with respect to the sensor body axis. A narrow pressure sensing orifice extends in parallel to the temperature sensing orifice. However, the inclined location of the temperature sensing element orifice results in a limited surface area for thermal exchange between the fluid media and the temperature sensor which is mostly embedded inside the sensor body. This hinders thermal transfer between a fluid media being measured and the temperature sensor and thereby results in a relatively slow temperature response.
U.S. Pat. No. 7,434,470 to Engelhardt et al. entitled Combined Pressure and Temperature Sensor describes a combined pressure and temperature sensor in which a pressure sensor is centrally disposed and temperature sensor is enclosed in a cover lobe which is substantially offset from the central axis. The offset location of the temperature sensor constrains access of fluid media to the temperature sensor. This results in a limited surface area for thermal exchange between the fluid media and the temperature sensor which is mostly embedded inside the sensor body, which hinders thermal transfer between the fluid media being measured and the temperature sensor, thereby resulting in a relatively slow temperature response.